With Seoul by-elections set to take place on the sidelines of the presidential election on March 9, the two main parties are looking to use their candidate selections to boost their chances in the main event.

Two Assembly seats are up for grabs in Seoul, and political heavyweights who fell in the presidential primaries are being eyed as possible candidates there, as party unity becomes a priority.

The two seats have been vacant since their lawmakers -- one from each of the two main parties -- stepped down.

The lawmaker seat in Jongno-gu has been empty since Lee Nak-yon left in September to focus on running in the ruling Democratic Party of Korea’s presidential primary. He came second, losing narrowly to Lee Jae-myung.

The Jongno-gu seat has historically been seen as having strong political significance, as the occupants have often strengthened their political footholds and chances of advancement to higher posts. Three former representatives of the constituency have gone on to become president.

The seat has often been used as a test of political mettle, with heavyweights from ruling and main opposition parties often facing off in elections there.

The Democratic Party is considering using the Jongno-gu candidate as a de-facto running mate for Lee, and is thought to be contemplating a Moon administration heavyweight to increase the party’s chances of victory.

Former presidential chief of staff Im Jong-seok, one of President Moon Jae-in’s closest aides, is widely touted as a potential candidate. The head of the Foundation of Inter-Korean Cooperation has held major key posts for the ruling party and has served as a lawmaker in Seongdong-gu in the past.

Aside from Im, former Justice Minister Choo Mi-ae is another possible ruling party candidate, due to her high-level of public recognition. As minister, the former party leader oversaw prosecutorial reform, and she was a five-term lawmaker for a constituency in Gwangjin-gu, eastern Seoul.

Choo is currently on Lee’s presidential campaign team, having lost to him in the presidential primary.

Former SMEs Minister Park Young-sun is also mooted as a possible candidate for the same party. But Park has made no noticeable political moves since losing the Seoul mayoral by-election to Oh Se-hoon in April.

The main opposition People Power Party is expected to field its chairman, Lee Jun-seok, who has won support from young voters as a symbol of change. But Lee is known to be more interested in running for in Nowon-gu, northern Seoul, where he has previously run three times, albeit unsuccessfully.

As the People Power Party’s presidential nominee Yoon Seok-youl looks to unify the party for his presidential campaign, one option to help him in this regard is for one of his presidential primary rivals to be chosen for the Jongno-gu constituency.

Yoon competed against Rep. Hong Joon-pyo, former Jeju Province Gov. Won Hee-ryong and former Rep. Yoo Seong-min in the final stage of the primary race, all of whom have been discussed in local media outlets as possible Jongno-gu contenders.

Former audit agency chief Choe Jae-hyeong, who competed against Yoon in the earlier stage of the primary race, could also be considered as a candidate for the constituency, as well as presidential candidates from other parties if the People Power Party unites with them for the presidential election.

The other legislative by-election is in Seocho-gu, southern Seoul, which has had no lawmaker since Yun Hee-suk from the People Power Party resigned in August over an alleged land speculation deal involving her father.

The Seocho-gu constituency has been traditionally been a safe seat for the conservative party, and the People Power Party is considering two female officials in choosing its candidate there.

The party is expected to announce former Rep. Jun Hee-kyung as the official organizer for Seocho-gu constituency election on Thursday. Whoever takes the organizer post has traditionally been selected as the candidate for the election.

Jun was spokesperson for the party and ran unsuccessfully for an Assembly seat in Incheon last year.

Jun is set to internally compete with Cho Eun-hee, the former head of the Seocho-gu district government, who stepped down from the post Tuesday to run in the by-election. She became the first female vice mayor for Seoul in 2010 and has served as district governor since 2014.

The party has unfavorably viewed Cho’s resignation and is thought to have asked her to stay on as district governor, as she was the only district governor representing the main opposition party in Seoul. All other 24 district governors are associated with the Democratic Party.

Cho was reported to have announced her resignation without consulting the party.

It is unclear who the ruling party will pick to run for the constituency, but Lee Jung-geun, a party member who made three unsuccessful election bids in the district, is believed to be eyeing another attempt.

She fell behind Cho in the 2018 election for district governor and came in second place for the Seocho-gu constituency in two consecutive parliamentary elections in 2016 and 2020.